A typical walk-behind soil compactor includes a frame that carries a generally horizontal compaction plate which is adapted to engage and compact soil or other material. To provide vibratory compacting action, one or more eccentric shafts are journaled for rotation on the frame and a power source, such as a gasoline engine, is mounted on the frame. The drive shaft of the engine is operably connected to the eccentric shafts to rotate the eccentric shafts and provide the vibratory motion.
A walk-behind compactor can either be unidirectional, in which the compactor will move only in a single direction over the terrain, or it can be bidirectional or reversible. In a conventional reversible soil compactor, the engine drive shaft is connected to the eccentric shafts through a gear train, which is arranged so that the eccentric shafts rotate simultaneously and in opposite directions. To provide forward and rear movement for the compactor, the phase relationship of the weights on the eccentric shafts is changed by a shifting mechanism. The typical shifting mechanism is very complex and as it is directly associated with the eccentric shafts, the shifting mechanism is subject to intense vibration, and therefore has a relatively short service life.
As a further problem, the eccentric shafts are continuously rotating in opposite directions, so that torque generated by one shaft will oppose the torque generated by the second eccentric shaft. Because of this, and the weight resulting from the complex shifting mechanism, the speed of travel of the compactor is substantially reduced over a similarly powered unidirectional compactor.
U.S. Pat. No. 5,149,225 is directed to an improved, reversible, walk-behind compactor, in which a reversible clutch is associated with the drive shaft of the engine and selectively connects each eccentric shaft via a separate drive belt to the drive shaft. The drive belts are arranged so that the eccentric shafts are rotated in opposite directions, but not simultaneously. With the construction of the aforementioned patent, only one drive belt is engaged at any instant, so that the torque generated by one eccentric shaft does not oppose or fight the torque generated by the second eccentric shaft, thus enabling the speed of travel to be increased with the same power input.
U.S. patent application Ser. No. 07/894,527, filed Jun. 5, 1992, discloses an improved reversible drive mechanism for a walk-behind vibratory compactor. A reversible clutch is associated with the drive shaft of the engine and selectively connects the drive shaft, via separate drive belts, to the respective eccentric shafts. The drive belts are arranged so that the eccentric shafts operate in opposite directions. By connecting one of the eccentric shafts to the drive shaft, the compactor will move in a forward direction and conversely, by connecting the other of the eccentric shafts to the drive shaft, the compactor will move in a reverse direction.
During a period of use the separate drive belts, as used in the construction of U.S. Pat. No. 5,149,225, and the aforementioned patent application, will tend to loosen, and tension on the belts is adjusted by moving the engine, including the drive shaft, both in a vertical direction and in a horizontal direction. As adjustment of the tension on one belt effects the tension on the other belt, it is a very difficult and time consuming task to properly adjust the tension for both of the drive belts.